334 SEX IN A4ICROORGANISA/IS 



reactions are never observed when the types are mixed. These investigators 

 suggest that conjugation may be mediated by substances released into the me- 

 dium by the organisms. These papers give an account of the cytology of 

 conjugation in the Woods Hole stocks and in a third paper Nanney (1953) 

 describes the conjugation cytology, including the conjugation of three animals, 

 and the effects of centrifugation on nuclear development of conjugants in a 

 selfing stock (AA 1-8). 



Unlike certain P. mirelia stocks which ordinarily mate only at night and 

 are inhibited by light (Sonneborn, 1938a), P. hursaria generally mates onh' 

 during the day. However, Ehret (1953) finds that animals maintained in con- 

 tinuous darkness exhibit the normal rhythm but with reduced intensity. The 

 reactive period may be shifted and its intensity enhanced or diminished by 

 appropriate exposure to light. The action spectrum for these effects suggests 

 a flavin type photosensitive substance. Ehret presents quantitative ultraviolet 

 and x-ray inactivation data for mating reactivity and describes a phenomenon, 

 "autoagglutination" (sticking together of animals of the same mating type), 

 which results from ultraviolet, x-irradiation, or high-intensity visible irradia- 

 tion. Since this reaction may be induced in unreactive and immature clones and 

 is associated with various pathological changes (vesiculation, bleb formation, 

 immobilization), its relation, if any, to the specific mating reaction is problem- 

 atical. It would not appear to be related to the x-ray induced change of 

 mating type reported by Lee (1949). The observation that formalin killed 

 P. biirsaria give mating reactions (Metz and Foley, 1949) takes some force 

 from Ehret's hypothesis that mating substance is continuously lost and synthe- 

 sized anew at the cilium surface during the reactive phase. 



REFERENCES 



Ehret, C. F. 1953. An analysis of the role of electromagnetic radiations in the 

 mating reaction of Farmnechmi bursaria. Phys. Zool., 26, 274. 



Elliott, A. M., and R. E. Hayes. 1953. Mating types in Tetrahyineiia. Biol. 

 Bull, 105, 269. 



Lee, H. 1949. Change of mating type in Faraiiieciwn bursaria following ex- 

 posure to x-rays. /. Exptl. Zoo/., 112, 125. 



Nanney, D. L. 1953. Nucleo-cytoplasmic interaction during conjugation in 

 Tetrahyiiiena. Biol. Bull., 105, 133. 



Nanney, D. L., and P. A. Caughey. 1953. Mating type determination in Tctra- 

 loyviena pyriformis. Proc. Natl. Acad. Sci. U. S., 39, 1057. 



Runnstrom, J. 1952. The cell surface in relation to fertiHzation. Syvip. Soc. 

 Exptl. Biol, 6, 39. 



